1. Field of the Invention
The present invention relates to a retransmission control method and device, and in particular to a method and device for controlling a retransmission of user data using an RLC (Radio Link Control) protocol.
2. Description of the Related Art
Prior art examples of such a retransmission control technology will now be described referring to FIGS. 12, 13A-13C, 14, and 15.
A radio communication system 1 shown in FIG. 12 is composed of a core network 10, a radio network control device 20 connected to the core network 10, a base station 30 managed by the radio network control device 20, and a user equipment (user terminal) 40 connected to the radio network control device 20 through the base station 30 to perform a packet data communication.
As shown in FIG. 13A for example, the packet data communication in the radio communication system 1 is performed, in which the radio network control device 20 on the transmitting side divides packet data SDU (Service Data Unit) into user data AMD_PDU (Acknowledged Mode Data Protocol Data Unit) of a size prescribed by the RLC protocol to be transmitted, and the user equipment 40 on the receiving side assembles (not shown) the original packet data SDU from the received user data AMD_PDU.
It is to be noted that while the radio network control device 20 and the user equipment 40 are respectively supposed to be on the transmitting side and the receiving side of the user data in order to simplify the description in the prior art example, the description hereinafter can be similarly applied to the reverse case where only the flow of the signal is reversed.
Also, the RLC protocol is for realizing both functions of a delivery acknowledgment (ACK) control and a retransmission control which will be described later for the user data AMD_PDU transmitted/received between the radio network control device 20 and the user equipment 40.
Delivery Acknowledgment Control: FIGS. 13A-13C
The format of the user data AMD_PDU includes, as shown in FIG. 13B, a data type D/C indicating whether the data is user data or control data which will be described later, a sequence No. SN indicating a connection sequence of divided user data, a polling bit P indicating whether or not the delivery acknowledgment control for the data is validated, an area HE storing a user data length or the like, length/indicator LI, a bit E, a data area DT storing data entity, and a padding PAD (or piggyback).
The radio network control device 20, as shown in FIG. 13A, divides the packet data SDU into e.g. three user data AMD_PDU0-AMD_PUD2, and assigns thereto sequence Nos. SN (“0000”-“0002”) respectively to be sequentially transmitted to the user equipment 40.
Also, in order to perform the delivery acknowledgment control of the user data AMD_PDU0-AMD_PDU2, the radio network control device 20 sets the polling bit P of the last user data AMD_PDU2 “1” (valid) to be transmitted, which is made the delivery acknowledgment request (hereinafter, occasionally referred to as ACK request) for the user data AMD_PDU0-AMD_PDU2.
Supposing that all of the user data AMD_PDU0-AMD_PDU2 are normally transmitted/received, the user equipment 40 generates control data CTRL_PDU indicating a response (hereinafter, occasionally referred to as ACK response) to the ACK request to be transmitted to the radio network control device 20.
It is to be noted that for simplifying the figures, the ACK request and the ACK response in the attached figures are described in parentheses, which are added to the reference characters of the user data AMD_PDU including the ACK request and the control data CTRL_PDU indicating the ACK response, respectively. Hereinafter, the ACK request and the ACK response will be similarly described in the attached figures.
The format of the control data CTRL_PDU includes, as shown in FIG. 13C, a data type D/C indicating whether the data is the user data or the control data, a control type C_TYPE (where e.g. a reset RESET, a status report STATUS, or the like is set) indicating the control type of the data, a variable length decoding field SUFI, and a padding PAD. The decoding field SUFI is composed of an information type I_TYPE indicating a type of information added to the data, its information length “Length”, and an information data area “Value” storing information entity.
It is to be noted that in this example, “status report STATUS” and “delivery acknowledgment ACK” are respectively set in the control type C_TYPE and the information type I_TYPE of the control data CTRL_PDU, and serial Nos. SN={0000, 0001, 0002} of the user data AMD_PDU0-AMD_PDU2 received by the user equipment 40 are set in the information data area “Value”.
The radio network control device 20 having received the control data CTRL_PDU indicating the above-mentioned ACK response confirms whether or not the user data AMD_PDU0-AMD_PDU2 transmitted by the radio network control device 20 itself are normally delivered by referring to the control data CTRL_PDU.
Since the serial Nos. SN of all of the user data AMD_PDU0-AMD_PDU2 are set in the information data area “Value” within the control data CTRL_PDU in this example, the radio network control device 20 determines “normal (OK)” as a result of the delivery acknowledgment.
Retransmission Control: FIGS. 14 and 15
Control examples [1] and [2] by the retransmission control function provided by the RLC protocol will now be described referring to FIGS. 14 and 15.
Retransmission Control Example [1] (Upon Polling Timeout): FIG. 14
After transmitting the ACK request for the user data AMD_PDU0-AMD_PDU2, as shown in FIG. 14, the radio network control device 20 issues a polling timer (TIM) which measures a predetermined time and waits for the ACK response from the user equipment 40.
For example, in the event that the ACK request (i.e. user data AMD_PDU2) for the user data AMD_PDU0-AMD_PDU2 is missing due to the influence of the communication failure or the like, as shown by a mark “X” in FIG. 14, the user equipment 40 can not transmit the ACK response to the ACK request to the radio network control device 20. Therefore, the polling timer (TIM) issued by the radio network control device 20 times out.
To be exact, when a timeout period T0 is fixed and there is no ACK response within the period, the radio network control device 20 regards that the ACK request for the user data AMD_PDU0-AMD_PDU2 transmitted is not normally received by the user equipment 40, so that the radio network control device 20 retransmits the user data AMD_PDU2 including the ACK request to the user equipment 40.
The user equipment 40 having normally received the user data AMD_PDU2 retransmitted generates the control data CTRL_PDU indicating the ACK response to the ACK request of the user data AMD_PDU0-AMD_PDU2 to be transmitted to the radio network control device 20.
The radio network control device 20 having received the control data recognizes that all of the user data AMD_PDU0-AMD_PDU2 are normally delivered, and determines “normal (OK)” as a result of the delivery acknowledgement.
Retransmission Control Example [2] (Upon List Reception): FIG. 15
When an omission of e.g. the user data AMD_PDU1 due to an influence of a communication failure or the like is detected within three user data AMD_PDU0-AMD_PDU2 transmitted from the radio network control device 20, as shown by the mark “X” in FIG. 15, the user equipment 40 generates the control data CTRL_PDU where the serial Nos. SN={0000, 0002} of the user data AMD_PDU0 and AMD_PDU2 normally received are set in the information data area “Value”, and transmits the control data to the radio network control device 20 as the ACK response to the ACK request from the radio network control device 20.
Concurrently, the user equipment 40 requests the radio network control device 20 to retransmit the user AMD_PDU1. This retransmission request is performed by transmitting the control data CTRL_PDU where list “LIST” is set in the information type I_TYPE, and the serial No. SN=“0001” of the user data AMD_PDU1 which requests the retransmission is set in the information data area “Value”.
The radio network control device 20 having received the above-mentioned retransmission request sets a polling bit P of the user data AMD_PDU1 to “1” (valid) to be retransmitted, and performs the ACK request for the user data AMD_PDU1.
The user equipment 40 having normally received the user data AMD_PDU1 retransmitted generates the control data CTRL_PDU indicating the ACK response to the ACK request of the user data AMD_PDU1 to be transmitted to the radio network control device 20.
The radio network control device 20 having received the control data recognizes that all of the user data AMD_PDU0-AMD_PDU2 are normally delivered, and determines “normal (OK)” as a result of the delivery acknowledgement.
Thus, by performing the delivery acknowledgment control and the retransmission control for the user data transmitted/received, a communication quality between the radio network control device and the user equipment is guaranteed (see e.g. patent documents 1-4).    [Patent document 1] Japanese Patent Application Laid-open No. 2002-271442    [Patent document 2] Japanese Patent Application Laid-open No. 2003-249974    [Patent document 3] Japanese Patent Application Laid-open No. 2005-65289    [Patent document 4] Japanese Patent Application Laid-open No. 2005-73251
Recently, an introduction of a high-speed packet data communication standard such as HSDPA (High Speed Down Link Packet Access) has been considered in a packet data communication in the radio communication system. Accordingly, the traffic of the packet data transmitted (namely, the user data that is the packet data divided) is increased, so that a processing congestion may frequently occur specifically on the receiving side of the user data.
In this case, although the receiving side normally receives the user data for the delivery acknowledgment request in the above-mentioned retransmission control example [1], the response is delayed (namely, the response can not be transmitted within a predetermined time), resulting in a problem that the retransmission of the user data from the transmitting side is unnecessarily performed.
In order to avoid this problem, it is possible to take measures by preliminarily setting the waiting time for the response longer for the delivery acknowledgment request on the transmitting side. However, when the omission of the user data actually occurs, the retransmission thereof is delayed (namely, essentially necessary retransmission is suppressed), so that the throughput on the receiving side is unnecessarily reduced.